<html>
<head>
  <style>
    div.slave { visibility:collapse; }
    widget.master:checked + div.slave { visibility:visible; }
  </style>  
<head>
<body>
  <widget type="checkbox" .master>First group:</widget> 
  <div .slave>
    <li>item #1</li>
    <li>item #2</li>
    <li>item #3</li>
  </div>
  <widget type="checkbox" .master>Second group:</widget> 
  <div .slave>
    <li>item #1</li>
    <li>item #2</li>
    <li>item #3</li>
  </div>
</body>
</html>